x86/kvm: On KVM re-enable (e.g. after suspend), update clocks (677a73a9) · Commits · 戴 / test

arch/x86/kvm/x86.c

+3 −72

Original line number	Diff line number	Diff line
		@@ -123,8 +123,6 @@ module_param(tsc_tolerance_ppm, uint, S_IRUGO \| S_IWUSR);
		unsigned int __read_mostly lapic_timer_advance_ns = 0;
		module_param(lapic_timer_advance_ns, uint, S_IRUGO \| S_IWUSR);

		static bool __read_mostly backwards_tsc_observed = false;

		#define KVM_NR_SHARED_MSRS 16

		struct kvm_shared_msrs_global {
		@@ -1671,7 +1669,6 @@ static void pvclock_update_vm_gtod_copy(struct kvm *kvm)
		&ka->master_cycle_now);

		ka->use_master_clock = host_tsc_clocksource && vcpus_matched
		&& !backwards_tsc_observed
		&& !ka->boot_vcpu_runs_old_kvmclock;

		if (ka->use_master_clock)
		@@ -7366,88 +7363,22 @@ int kvm_arch_hardware_enable(void)
		struct kvm_vcpu *vcpu;
		int i;
		int ret;
		u64 local_tsc;
		u64 max_tsc = 0;
		bool stable, backwards_tsc = false;

		kvm_shared_msr_cpu_online();
		ret = kvm_x86_ops->hardware_enable();
		if (ret != 0)
		return ret;

		local_tsc = rdtsc();
		stable = !check_tsc_unstable();
		list_for_each_entry(kvm, &vm_list, vm_list) {
		kvm_for_each_vcpu(i, vcpu, kvm) {
		if (!stable && vcpu->cpu == smp_processor_id())
		if (vcpu->cpu == smp_processor_id()) {
		kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
		if (stable && vcpu->arch.last_host_tsc > local_tsc) {
		backwards_tsc = true;
		if (vcpu->arch.last_host_tsc > max_tsc)
		max_tsc = vcpu->arch.last_host_tsc;
		}
		kvm_make_request(KVM_REQ_MASTERCLOCK_UPDATE,
		vcpu);
		}
		}

		/*
		* Sometimes, even reliable TSCs go backwards. This happens on
		* platforms that reset TSC during suspend or hibernate actions, but
		* maintain synchronization. We must compensate. Fortunately, we can
		* detect that condition here, which happens early in CPU bringup,
		* before any KVM threads can be running. Unfortunately, we can't
		* bring the TSCs fully up to date with real time, as we aren't yet far
		* enough into CPU bringup that we know how much real time has actually
		* elapsed; our helper function, get_kernel_ns() will be using boot
		* variables that haven't been updated yet.
		*
		* So we simply find the maximum observed TSC above, then record the
		* adjustment to TSC in each VCPU. When the VCPU later gets loaded,
		* the adjustment will be applied. Note that we accumulate
		* adjustments, in case multiple suspend cycles happen before some VCPU
		* gets a chance to run again. In the event that no KVM threads get a
		* chance to run, we will miss the entire elapsed period, as we'll have
		* reset last_host_tsc, so VCPUs will not have the TSC adjusted and may
		* loose cycle time. This isn't too big a deal, since the loss will be
		* uniform across all VCPUs (not to mention the scenario is extremely
		* unlikely). It is possible that a second hibernate recovery happens
		* much faster than a first, causing the observed TSC here to be
		* smaller; this would require additional padding adjustment, which is
		* why we set last_host_tsc to the local tsc observed here.
		*
		* N.B. - this code below runs only on platforms with reliable TSC,
		* as that is the only way backwards_tsc is set above. Also note
		* that this runs for ALL vcpus, which is not a bug; all VCPUs should
		* have the same delta_cyc adjustment applied if backwards_tsc
		* is detected. Note further, this adjustment is only done once,
		* as we reset last_host_tsc on all VCPUs to stop this from being
		* called multiple times (one for each physical CPU bringup).
		*
		* Platforms with unreliable TSCs don't have to deal with this, they
		* will be compensated by the logic in vcpu_load, which sets the TSC to
		* catchup mode. This will catchup all VCPUs to real time, but cannot
		* guarantee that they stay in perfect synchronization.
		*/
		if (backwards_tsc) {
		u64 delta_cyc = max_tsc - local_tsc;
		backwards_tsc_observed = true;
		list_for_each_entry(kvm, &vm_list, vm_list) {
		kvm_for_each_vcpu(i, vcpu, kvm) {
		vcpu->arch.tsc_offset_adjustment += delta_cyc;
		vcpu->arch.last_host_tsc = local_tsc;
		kvm_make_request(KVM_REQ_MASTERCLOCK_UPDATE, vcpu);
		}

		/*
		* We have to disable TSC offset matching.. if you were
		* booting a VM while issuing an S4 host suspend....
		* you may have some problem. Solving this issue is
		* left as an exercise to the reader.
		*/
		kvm->arch.last_tsc_nsec = 0;
		kvm->arch.last_tsc_write = 0;
		}

		}
		return 0;
		}

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